hello,
I will first tell you my story with my n9...
3 weeks ago, I got a brand new nokia n9 from a friend who works at nokia. I open it, switch it on, update it.
=> works nice !
then, many times by week, I get an update which I install without worring.

last week, I got an update notification for 30.2012.01-3 + facebook app update which I delayed. later, I try to install them : impossible. I get this error :

Can't complete the download. Connection to the application provider was lost. Try again later.

I tried different wifi networks, my cellular network, different times of the day : still doesn't work ! I tried to enable developer mode : it can't install the required packages (same error).

I do some research : surprise ! looks like everybody is still on pr1.1 while mine is running pr1.2 (30.2012.01-2)...
I install file manager and check /etc/apt/sources.list.d/aegis.ssu-keyring-001.list and I found the explanation :